Color cathode-ray tube and assembly process



1957 L'. F. CRAMER ET AL COLOR CATHODE-RAY TUBE AND ASSEMBLY PROCESS 2 Sheets-Sheet 1 Filed Nov. 5, 1954 INVENTORS. LEONARD E GRAMER. RICHARD A MAHER.

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ATTORNEYS.

1957 L. F. CRAMER ET AL COLOR CATHODE-RAY TUBE AND ASSEMBLY PROCESS Filed Nov. 3, 1954 2 Sheets-Sheet 2 INVENTORS MAHER.

. L-EONARD F. cRAMR. BY RICHARD A Unite States Patent G COLOR CATHODE-RAY TUBE AND ASSEMBLY PROCESS Leonard F. Cramer and Richard A. Maher, Cincinnati, Ohio, assignors to Avco Manufacturing Corporation, Cincinnati, Ohio, a corporation of Delaware Application November 3, 1954, Serial No. 466,548

' 3 Claims. (Cl. 313-78) 1 This invention relates, in general, to cathode-ray tubes and specifically to cathode-ray tubes of the type useful in reproducing color images.

Electron beam control requirements in a color .type cathode-ray tube are far more critical than beam control requirements in a cathode-ray tube of the black and white image reproducing type, due to the fact that the electron beam must strike a discrete primary col-or phosphor area at the instant that the signal is carrying the corresponding primary color information. One .tube designed to. solve the problem uses a control or switching grid adjacent to the phosphor screen for providing a postdeflection beam deflecting force.

In the grid-switching type of tube little, if any, effort has been made to utilize the face plate end of the cathoderay tube envelope as a screen surface. In lieu of using this available surface, as is done in blackand white tubes, it has been considered necessary to provide a sofcalled color pack, comprising a frame-supported grid and plate glass screen element upon which the phosphors are placed. The expense of this color pack and the cost of supporting it in a tube envelope has made the gridswitching type of tube relatively expensive for commercial home television use.

Thus, it is an object of this invention to provide a gridswitching type of color cathode-ray tube which utilizes a glass-to-metal seal with the tube envelope wall to support each grid wire and which uses the internal face plate surface of the envelope as a screen.

It is also an object of this invention to provide a method of fabricating a commercial type of grid-switching cath ode-ray tube useful in reproducing color images.

It is a further object of this invention to provide a grid-switching type of color tube which utilizes the full internal screen surface for reproduction of a color image.

It is a still further object of this invention to provide a grid-switching type of color cathode-ray tube which is light in weight, easily shielded and simple enough to be feasible for commercial mass production.

Briefly, the invention comprises a grid-switching cathode-ray tube of the color type, wherein each switching grid wire is sealed at both ends into the wall of the .tube envelope. Where the wall of the tube envelope is too thin or too weak to completely support the grid, an additional external frame is provided. Electrical contact to the grid can be either external orinternal.

For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following 'disclosure and appended claims in connection with the accompanying drawings, in which:

Fig. 1 shows the switching grid as used in a color tube with horizontal phosphor lines, and

Fig. 2 shows a cutaway view of the tube and Fig. 3 is a schematic representation showing the electrical connection to the grid, and j I... Fig. 4 shows a tube with external frame,.and

of Fig. 1,

2,813,213 Patented Nov. 12,1957

Fig. 5 schematically represents a simple method of assembling the tube, and

Fig. 6 shows an alignment of grid wires in a tube where the phosphor strips on the screen surface are aligned vertically.

In Fig.. 1, as an aid in teaching the invention, there is shown a preferred embodiment comprising a cathode-ray tube envelope 11 with conventional base 12, electrode connecting pins 13 and a conventional electron gun 14. These elements, as well as other elements common to all of the figures shown, will be identified by the same notations throughout all figures. In the cutaway portion of Fig. 1, the grid wires 15 can be seen to be positioned adjacent to the face plate end 16 of the tube envelope, the internal surface 17 of which is used for the phosphor screen.

Each of the wires of grid 15 are sealed at both ends by a glass-to-metal seal in the tube envelopewall, and, in this particular embodiment, external contacts are shown. Contact electrodes 18 are attached to alternate grid wires and insulated from contact electrodes 19 which are attached to the remaining gridwires.

It may be assumed that contacts 18 are connected to the odd-numbered grid wires while electrodes 19 are connected to the even-numbered grid wires. An enlarged schematic type drawing of these connections is found in Fig. 3, where it can be seen that the odd-numbered grid wires are ,bent along the surface of the envelope wall in one direction, while the even-numbered wires are bent along the tube envelope wall in the opposite direction. Thus, electrodes 18 and 19 may be soldered, pressed or welded into place with suflicient spacing to afford the necessary inter-electrode insulation, but without such excessive spacing as to make the shielding problem difficult.

In Fig. 2 this tube is shown cut along a plane between the grid surface and the rear conical portion of the tube envelope. The actual number of grid wires used depends upon the number of phosphor line elements provided in that any number of grid wires may be thus supported,

so long as a tube envelope of sufiicient strength at the sealing points is used.

Where the tube envelope wall at the grid wire sealing points is too thin to support the grid structure, as may be the case in a rectangular tube with vertically aligned grid wires and phosphor strips, an external grid frame may be used, as schematically represented in Fig. 4. Thus, frame 20 provides a strong termination support for each grid wire and is capable of carrying a large percentage of the stress which would otherwise be imposed by grid wire tension on the tube envelope alone.

The electrical connections to the grid wires may be made either in a manner similar to that shown in Fig. 3 with grid-to-frame insulation being provided, or in the conventional manner presently used in internal mounted color packs.

Tensioning screws 22 are provided for dividing the total grid wire tension load between the tube envelope wall and the external frame. Since each grid wire is sealed into the tube envelope wall at both ends, adjustment of the tensioning screws 22 increases or decreases the tension of the wires between the external frame and the tube envelope wall. Thus, it is possible to minimize the stress on the tube envelope by bringing the effective internal grid tension load down to safe limits.

Support studs 23 may be provided on the external surface of the tube envelope. In the particular embodiment shown, studs 23 are positioned to be slidably attached to the grid frame so as. to allow movementof the frame relative to the tube envelope ina direction to either increase or decrease grid wire tension. Other support means will occur to those skilled in the art.

The grid-switching tube of the type herein disclosed can be assembled by the tube envelope manufacturer by adding a relatively small number of steps to the present process for constructing tube envelopes. As shown in Fig. 5, the face plate portion of the tube may be mounted in a supporting chuck 24 and the grid wires stretched across an assembly frame 25. By placing the face plate portion of the tube envelope on one side of grid and the conical portion of the envelope 11 on the other side of the grid wires, it is possible to apply heat to the grid-tube envelope juncture to form the desired metalto-glass and g'lass-to-glass seals. In some cases it may prove desirable to use a grid frame, either temporary or permanent, tostretch the grid 15 over either the face plate portion or the conical portion 11 of the tube envelope and apply heat in order first to form a metal-to-glass seal between the grid wires and the wall of the tube envelope. Then, as a second step, the remaining portion of the envelope may be brought into axial alignment with the remaining tube'envelope portion, and heat applied to form the glass-to-glass seal to complete the envelope structure. Then, if an external grid frame is not to be used, the external grid wires are clipped and the temporary grid frame removed.

This method is not to be considered as restricted to cathode-ray tubes having a glass envelope, even though it is essential that the grid wires either terminate or extend through the tube envelope at a glass sealing point. It is possible, in those cases where a metal envelope is desired, as well as in some cases where a glass envelope is used, toprovide a glass doughnut-shaped structure into which the grid wires are first sealed. The resulting grid structure is then framed in a glass ring which can be inserted between the face plate portion of the tube envelope and the conicalendportion of the envelope, with appropriate seals being made to complete the tube envelope. Where the conical portion of the envelope is metal, a metal-to-glass seal is required between the glass grid-supporting ring and the conical end of the tube envelope. Where the face plate portion of the tube envelope also includes a metal ring which terminates at the grid sealing point, an additional metal-to-glass seal is required between the metal face plate ring and the glass grid-supporting ring. Where both the face plate portion and the conical portion of the tube envelope are glass, the three portions of the complete envelope are all joined by glass-to-glass seals.

The grid 15 may be wound on a frame, such as frame 2% of Fig. 4, prior to the tube envelope assembly operation. Even, in those cases where an external frame is not necessary, the grid may be wound on a temporary frame in the manner taught in U. S. Patent No. 2,800,929 to Warner et al. Briefly, the method contemplated in the Warner et al. patent provides a cylindrical mandrel having recessed slots into which end plates 27, as shown in Fig. 5, may be first inserted. The mandrel surface is grooved in thread-like fashion with either a linear or varying pitch to provide mechanical means for positioning the grid wires relative to each other, and this, when utilized with asynchronized' rotating grid wire screw feed, provides a rapid commercial assembly method. For a further and more detailed understanding of this method of fabricating the; grid structure, reference is made to the aboveentioned Warner et al. patent.

After the tube envelope is assembled in the manner shown in Fig. 5, the grid wires may be cut flush with the external tube envelope wall on either or both sides, depending upon the type of electrical grid contact desired. External grid-contacts of the type shown in Figs. 1

,through 3 require a small length of grid wire to protrude .throughthe envelope wall, and in tubes where such a contact is used, the 'gridwire should be cut accordingly,

t o,pro vide a given length of wire external to thetube 4 envelope. In tubes where an internal electrical contact of the type presently used in color packs is desired, the contact must be provided internally prior to final assembly, and the grid wires cut flush with the outside surface of the tube envelope wall.

This method of fabricating the tube envelope is especially useful where a grid is desired which is curved in one dimension so as to be substantially parallel in that dimension with the internal surface of the face plate end of the tube envelope, as shown in Fig. 6. The electron-optical errors which require compensation in units using a flat grid can be eliminated, to a large extent, by the expedient of curving the grid surface.

After the tube is assembled, the phosphors may be deposited on the internal face plate end of the tube by conventional photographic processes now used in conjunction with tubes of the shadow mask type. Positioning of the electron gun and connection of the tube base incorporating the gun electrode-connected pins can be done in conventional manner.

The final assembled tube, as can be seen from the drawings, allows the entire internal surface of the face plate end of the tube to be used for image reproduction. This is to be contrasted with other color tubes, presently being built, which invariably use a considerable portion of the internal tube volume for internal grid-supporting structures, and thus encroach on what would otherwise be useful screen area. Variations in individual grid wire tension during assembly are relatively unimportant, due to the fact that other conventional processes necessary for completion of the tube, such as the phosphor screen bake'out cycle and other heating cycles, are of suificiently high temperature to stabilize and equalize individual grid wire pull against thetube envelope seal.

The increased economy in manufacturing and the increased performance characteristics made possible by the efficient use of the full face plate area for image reproduction make the final tube practical for mass production and sale in home television receivers.

While there has been shown and described what is at present considered the preferred embodiment of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the ap pended claims.

Having thus described the invention, we claim:

1. In a cathode ray color television tube of the grid switching type, the combination of a glass envelope, having a neck portion and a screen portion, an electron gun positioned in the neck portion-of the tube envelope, an external grid frame surrounding the tube envelope, a plurality of parallel taut grid wires, each disposed adjacent the internal envelope screen surface and transverse to the longitudinal axis of the tube envelope, both ends of each grid wire extending through the tube envelope wall in a metal-to-glass seal, means attaching both ends .of each grid wire to the external grid frame, with the odd-numbered grid wires being electrically insulated from the even-numbered grid wires.

2. In a cathode ray color television tube of the gridswitching type, the combination of a glass envelope, an electron gun supported in the neck portion of the tube envelope, a plurality of parallel taut grid wires disposed in a plane transverse to the longitudinal axis of the tube envelope and adjacent the internal envelope screen. surface, each grid wire being sealed into the wall of the glass envelope at both ends with at least one end of each grid wire extending through the tube envelope wall, means external to the tube envelope for electrically interconnecting all odd-numbered grid wires to one electrode and means external to the tube envelope for electrically interconnecting all even-numbered grid wires to the second electrode.

3. In a cathode ray color television tube of the gridswitching type,xthe combination of a glass envelope, an

5 6 electron gun supported in the neck portion of the tube References Cited in the file of this patent envelope, at plllhralilty oft zlatralllel tautfgfild wiges disposer; UNITED STATES PATENTS ransverse o e ongi u ma ans 0 e u e enve op and adjacent the internal envelope screen surface, each 1,038310 f Lleben et a1 "g ggrid wire being sealed into the wall of the glass envelope 5 1,087,180 Pierce Z; 9 at both ends with at least one end of each grid wire ex- 11904436 Fralnklln g 1 1933 tending through the tube envelope wall, means external 1,975,714 Da lenbach 1934 to the tube envelope for electrically interconnecting all 2,074,864 szflzberg 1937 odd-numbered grid wires to one electrode and means ex- 2151781 Lmdenblad 28, 1939 ternal to the tube envelope for electrically interconnecting 10 2,153,728 Southworth 1939 all even-numbered grid wires to a second electrode. g fi g 2,695,372 Lawrence Nov. 23, 1954 

